The present invention concerns fluid process transmitters used in industrial fluid processing plants. In particular, the present invention concerns process sensor modules used in process transmitters.
In pressure transmitters, there are usually two separate housings that are assembled. One of the housings is a sensor module housing which has piping connections for pressure fittings, and includes the actual pressure sensor and a circuit board that has electronic components on it. The second housing is the electronics assembly housing that includes a circuit board having additional circuit components, and includes one or more threaded conduit hubs for connecting conduits carrying a communication bus to the pressure transmitter. A multiconductor cable passes through interior openings between the housings and connects the circuit boards.
Generally, the first (sensor) housing is rigidly mounted to the pressure fittings, and the second (electronics) housing is able to rotate relative to the first housing. This allows a conduit hub on the second housing to be conveniently connected to a conduit that carries the communication bus. One arrangement for providing this rotation ability is shown in U.S. Pat. No. 5,028,746 Petrich.
As more miniaturized integrated circuits that operate at lower voltages have become available, there is a desire to use them to reduce the size and power consumption of the sensor module. There is a problem, however, with the higher level signals and noise of the communication bus passing via the multiconductor cable into the lower power integrated circuits. The signal-to-noise ratios are degraded because of the reduced power or signal levels in the sensor electronics, and the lower level integrated circuits can""t be used because of the noise.
Finding a solution to the noise problem is difficult. There are multiple conductors to be shielded or filtered. Also, a wider variety of noise scenarios are encountered as more communication bus protocols are introduced. Some communication busses have one lead grounded (xe2x80x9csingle-endedxe2x80x9d lines) and some communication busses have neither lead grounded (xe2x80x9cbalancedxe2x80x9d lines). Each communication protocol also has its own range of signal frequencies that each present different noise problems to be dealt with.
In other process transmitters, such as temperature, pH and flow transmitters, problems are encountered that are analogous to the problems described above with with respect to pressure transmitters.
Process transmitters are needed that are rotatably connectable to a wide variety of communication bus protocols and that avoid conducting excessive noise to the sensor module so that lower voltage level integrated circuits can be used in the sensor module.
A process sensor module includes a housing with a first fitting that rotatably mates with a corresponding fitting on a bus adapter module. Integrated circuitry in the housing includes a process sensor. A two conductor circuit energizes the integrated circuitry, communicates a sensed process variable to the bus adapter module and communicates data from the bus adapter module to the integrated circuitry. A rotatable coaxial electrical contact is sealed in the first fitting and connects the two conductor circuit to the bus adapter module.